Field of the Invention
The invention relates to a method for producing circuit structures on a semiconductor substrate with the aid of a lithography process. Photoresist structures are formed on the semiconductor substrate in order to define dummy circuit structures. The invention also relates to a semiconductor configuration with functional circuit structures and dummy circuit structures produced with the aid of the lithography process.
A lithography process is usually utilized to produce circuit structures on a semiconductor substrate. The lithography process essentially includes the structuring of a masking layer, commonly SiO2, through a structured photoresist. In order to produce the structured photoresist, the resist is applied to the masking layer and then exposed and developed through an exposure mask, so that photosensitive structures remain on the masking layer. The photoresist structures cover particular regions of the masking layer and leave exposed regions, in which the masking layer is accessible for a subsequent etching step by which the masking layer is structured.
The exposure of the photoresist in the lithography process is usually performed optically. As the smallest structures on the structured semiconductor substrate grow increasingly smaller, there are increasingly greater problems accurately reproducing the structures that are present on an exposure mask on a photosensitive layer. Because the structures on the exposure mask exhibit orders of magnitude in the range of the wavelength of the exposure radiation with which the resist is exposed, more intense diffraction effects occur at the margins of the structures. In particular, when the structures are disposed in regular patterns, the diffraction effects in the optical imaging through a diffraction grid on the exposure mask, which is formed by the structures, plays a significant role.
In order to purposefully control consequent deviations in the structure formation, dummy structures are usually provided, which are substantially without electrical function but which influence the characteristics of neighboring functional circuit structures in the production of the circuit. The dummy structures are provided predominantly in the margin region of field configuration of circuit structures, so that during production the functional circuit structures find the same environmental conditions at the margin as in the interior of the field.
It is accordingly an object of the invention to provide a method for producing circuit structures on a semiconductor substrate and a semiconductor configuraition with functional circuit structures and dummy circuit structures which overcome the above-mentioned disadvantages of the prior art methods of and devices of this general type, which has improved dummy circuit structures.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing circuit structures with an aid of a lithography process. The method includes the steps of providing a semiconductor substrate; forming photoresist structures on the semiconductor substrate to define dummy circuit structures; and forming further dummy circuit structures. Each of the further dummy circuit structures joins one of the dummy circuit structures that is smaller than a prescribed minimum size so that the prescribed minimum size is exceeded, the prescribed minimum size is determined by a smallest required adhering surface for photoresist forming the photoresist structures to adhere to the semiconductor substrate.
The dummy circuit structures can be very small in certain circuit structures, because it is frequently sufficient for purposes of avoiding margin-related deviations to place only parts of the circuit structures at the margin of a field configuration. But the result of this is that some of the dummy structures are smaller than the structures provided for the circuit structure, and the size of the dummy structures moves into dimensions in the range of the minimum structural size. When such small structures are structured with the aid of the lithography process, complications arise with the photosensitive masks. Specifically, the photoresist masks must be very small given small dummy structures, since the dummy circuit structures must be masked by correspondingly small photoresist structures when being produced by a lithography process.
The photoresist on the masking layer has only a limited adhesive power, and detachment from the masking layer can occur during production given very small photoresist structures. This causes the removal of the photoresist structures and/or their displacement to another location of the photoresist mask, which results in the covering of a region of the masking layer with respect to a subsequent step in which it should actually be uncovered. In all probability, this will substantially impair the functioning of the circuit, because, on one hand, given the omission of a dummy circuit structure, the function of the respective circuit structure at the margin may be impaired, or on the other hand, shorts or the like may occur if the photoresist structure is shifted to another location of the photoresist mask. The danger of detachment of the photoresist structure exists particularly when the joint surface of the photoresist structure is below a minimum structural size. The minimum structural size is defined by the area of the joint between the masking layer and be the photoresist layer given that the photoresist layer reliably adheres to the masking layer.
It is therefore inventively provided that the dummy circuit structure that is below the minimum structural size is joined to an additional dummy circuit structure, so that the minimum structural size is exceeded. This prevents the formation of photoresist structures of less than minimum structural size on the semiconductor substrate during the production process. The photoresist structure is thus prevented from detaching and moving to other regions of the semiconductor substrate, where it could impair the electrical function of the functional circuit structures.
According to an added mode of the invention, there is the step of joining one of the further dummy circuit structures to a respective one of the dummy circuit structures using a bridge structure.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a semiconductor configuration. The semiconductor configuration contains a semiconductor substrate, functional circuit structures disposed on the semiconductor substrate, and dummy circuit structures including first dummy circuit structures and second dummy circuit structures produced with an aid of a lithography process and disposed on the semiconductor substrate. Each of the first dummy circuit structures is joined to one of the second dummy circuit structures so that a minimum structural size is exceeded. The first dummy circuit structures are smaller than the minimum structural size, the minimum structural sized is determined by a smallest required adhering surface of photoresist utilized in the lithography process to adhere onto the semiconductor substrate.
According to an expedient embodiment, it can be provided that the joined dummy circuit structure is formed of two dummy circuit structures, each of which is smaller than the prescribed minimum size. The advantage of this is that the joined dummy structure can be kept optimally small, since the required minimum structural size is usually already achieved or exceeded by joining small dummy circuit structures. An optimally small joined dummy circuit structure is advantageous, since this also exerts an influence on the production of neighboring structures which may be adverse and should therefore by minimized.
According to another embodiment of the invention, it is provided that the functional circuit structures are disposed in a field, and that the dummy circuit structure is disposed at a margin of the field. The advantage of this is that the deviation of the functionality of the functional circuit structures situated at the margin owing to the different neighboring structures can be reduced.
According to another advantageous embodiment, it is provided that the functional circuit structures represent memory cells. With memory cells, in particular, it is necessary that the memory cells exhibit an identical functionality regardless of their position in the cell field. Furthermore, the cells in modern semiconductor memories are highly integrated, with the structural size being in the range of the smallest possible sizes that can be structured, i.e. near the minimum surface area as determined by the photoresist. In order to prevent deviations of the memory cells situated at the margin, it is necessary to provide dummy circuit structures whose surface area is smaller than the minimum surface area at the margin of a field containing the memory cells, because dummy circuit structures at the margin of a field often represent partial structures of the functional circuit structures.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for producing circuit structures on a semiconductor substrate and a semiconductor configuration with functional circuit structures and dummy circuit structures, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.